After a member hospital evaluated its infusion pumps, it found that
several pumps could not detect an occlusion in the upstream (bottle-side or proximal) IV
line. This problem can result when hospital personnel fail to release the upstream manual
clamp (if one is present) after activating the pump. Other mechanisms that can cause an
upstream occlusion are a clogged upstream filter or a nonvented bottle used with a
nonvented IV set. In these situations, some pumps will continue to operate, but the
patient will not receive the infusion.

Discussion

When the downstream (patient-side or distal) IV line is occluded, most
pumps alarm when the downstream line pressure exceeds a preset value. However, this
mechanism cannot detect an upstream occlusion. In this case, the pump not only can
continue to operate without infusing the solution, but it can also display an erroneous
value for the accumulated volume infused. This inaccurate record of total fluid volume
infused to the patient could result in an inappropriate clinical decision when prescribing
further IV therapy. It may also delay the administration of critical medications, which
can include both fast-acting drugs (e.g., dopamine, oxytocin, nitroprusside) and
slower-acting drugs whose effects are not immediately recognized (e.g., heparin, insulin,
lidocaine). The hospital reported that this situation has occurred with several patients
and has caused complications.

ECRI believes that undetected upstream occlusions may have other adverse
effects, although we have no documented reports of such occurrences. If a pump operates
without infusing any solution, the IV needle could become occluded by blood clots. In
addition, removing an IV set from the pump when an upstream vacuum pressure is present may
cause the vein at the infusion site to collapse due to the induced negative pressure.
These situations may sacrifice valuable venous infusion sites and complicate further IV
therapy.

Some currently sold infusion pumps can detect an upstream occlusion. The
most common detection mechanism is a drop (or flow) sensor. When the upstream IV line is
occluded and causes flow to cease, the absence of drops falling in the drip chamber causes
the unit to alarm. In addition to confirming fluid flow, drop sensors also can alert the
user to an empty IV container before the upstream IV line is depleted. This feature
eliminates the need for the user to prime a new IV set when replacing the IV solution
container.

Other mechanisms that can detect an upstream occlusion are also acceptable
and eliminate the problems associated with drop sensors (e.g., breakage, mispositioning,
nuisance alarms during patient transport). In cassette pumps that apply a negative
pressure to fill a cassette chamber, an upstream occlusion can be detected in one of two
ways: by monitoring for excessive negative pressure or by allowing the pump to stall when
the filling pressure exceeds the maximum pumping capability of the motor. (The latter
method is reliable only in pumps that alarm when the motor mechanism stalls.) In pumps
that passively fill a cassette chamber (i.e., by gravity flow), a sensor detects an
upstream occlusion by monitoring the presence of fluid in the filling chamber.

Another mechanism that can detect an upstream occlusion is an air-in-line
alarm. Residual air (e.g., minute air bubbles) may increase in volume significantly as the
negative pressure increases during an upstream occlusion; in some cases, enough air may
pass through the pumping mechanism to be detected by the alarm. Although most pumps are
equipped with an air-in-line detector, this mechanism's ability to detect upstream
occlusions is often unreliable.

The upstream occlusion detection performance (e.g., time to alarm at
different flow rates, maximum occlusion pressures, time to detect gradual occlusion
formation) may vary greatly with any of these different detection methods. For example,
the time to detect an upstream occlusion for those units with drop sensors may depend on
the set flow rate and the infusion pump alarm software. We will consider upstream
occlusion detection performance in a future evaluation of infusion devices. (See our
evaluation of infusion pumps in Health Devices 13:31-62.)

After investigating this problem
and surveying available infusion pumps, we found that six volumetric infusion pumps lack a mechanism
designed to detect an upstream occlusion. The probability that an upstream occlusion will occur
in such pumps depends on factors other than their intrinsic design. For example,
some IV sets are packaged with the roller clamp located just below the drip
chamber, which may increase the likelihood that the upstream occlusion will not be detected
when used with certain pumps. However, on other IV sets, the manual clamps, which
are located near the patient connection, will allow the upstream IV line to occlude only
if they are moved.

Although some pumps do not have an upstream detection mechanism, their
supplier states that its IV set product lines are nonetheless designed to be effective in
overcoming the upstream occlusion problem. All the manual clamps, except for burette and
blood administration IV sets, are located downstream of the cassette and cannot be moved
to the upstream IV line. The IV sets that do have upstream manual clamps have a drip
chamber below the clamps. An upstream occlusion due to a clamp that is inadvertently left
closed or to other mechanisms will be detected when the air in the drip chamber expands
and is pumped downstream to trigger the air-in-line alarm. Thus, IV set design in this
case may also be effective in preventing undetected upstream occlusions.

Some pumps can operate when the drop sensors are disconnected. Most such
pumps have a visual display that indicates when the drop sensor is not in use. Although
this feature allows the pumps to operate without being interrupted by nuisance alarms
during patient transport, manufacturers who incorporate this feature into their pump
design, as well as ECRI, believe that drop sensors on pumps so equipped should always be
used except during patient transport or when froth in the drip chamber obscures drop
detection.

When using infusion pumps that cannot detect upstream occlusions, it is
important to take proper precautionary measures. The risk of undetected occlusions is
greatly reduced by purchasing IV sets that have manual clamps on the downstream IV line
(and that cannot be repositioned to the upstream IV line). We recommend that upstream
manual clamps be moved to the downstream IV line and that IV sets with upstream manual
clamps that cannot be moved to the downstream IV line not be used unless they are required
by the pump manufacturer. However, these measures do not eliminate the need to provide
in-service training to emphasize this problem because several types of IV sets require
upstream clamps (e.g., primary set clamps for use with secondary lines, burette sets,
blood administration sets), and occlusions may be caused by other mechanisms.

Recommendations

Using the information provided in this report,
determine whether any pumps that are unable to detect an upstream occlusion
by their intrinsic design are in use at your hospital.

While this problem does not justify removing these
pumps from service, thorough training sessions focusing on undetected
upstream occlusions should be provided for all users. Although failing to
release a manual clamp is the most likely cause of upstream occlusions,
inform users that an upstream occlusion can also occur when an upstream
filter becomes clogged or a nonvented IV bottle is used with a nonvented IV
set.

Provide periodic in-service training to remind
staff of this problem as well as all other aspects of pump operation.

When possible, use IV sets that have downstream
manual clamps for all pumps, and instruct users to position manual clamps on
the downstream IV line.

If the manufacturer does not provide a cautionary label, prominently
place a notice such as the following on all infusion pumps:
Check fluid flow after activating the pump and hourly thereafter.
While labels cannot guarantee that accidental
upstream occlusions will not occur, but they may help reduce their
frequency.

In selecting new pumps, keep the advantages of detecting upstream
occlusions in perspective along with other safety concerns, pump
performance, and economic factors.